1. Field of the Invention
The present invention relates to a paper type determination device used in a printer or a copying machine to determine the type of paper as a recording material subjected to printing, and an image forming apparatus using the paper type determination device.
2. Description of the Related Art
With an electrophotographic image forming apparatus, such as a copying machine and a laser printer, the type of paper used as a recording material is automatically determined and the developing condition, the transfer condition, or the fixing condition is changed according to the determined paper type.
As a device that determines the paper type, there are devices disclosed in Japanese publications of unexamined applications described in the following.
In the device described in a Japanese publication of unexamined application, JP-A-2006-117363, light is irradiated to a first surface of a recording material and an image of the first surface of the recording material is taken and light is irradiated to a second surface of the recording material and an image of the first surface is taken by an imaging device. The surface roughness is detected from the images of the recording material taken by the imaging means, and the surface roughness thus detected is compared with an initial setting threshold value used to determine plural recording materials to determine which one of the plural recording materials is the paper type of the recording material on the basis of the comparison result.
In the device disclosed in another Japanese publication of unexamined application, JP-A-2006-23288, first irradiation means for irradiating light to a recording material to obtain reflected light from the surface of the recording material is provided, and second irradiation means for irradiating light to the recording material to obtain transmitted light from the recording material is provided. In addition, reading means for reading specularly reflected light and diffusively reflected light reflected on the recording material as the result of irradiation from the first irradiation means, and specularly transmitted light and diffusively transmitted light having passed through the recording material as the result of irradiation from the second irradiation means are provided separately. The type of the recording material is determined using a ratio of reflected light of an amount of specularly reflected light and an amount of diffusively reflected light and a ratio of transmitted light of an amount of specularly transmitted light and an amount of diffusively transmitted light obtained by these means.
Further, the device disclosed in still another Japanese publication of unexamined application, JP-A-2005-75469, irradiates light to a recording material to measure light specularly reflected on the recording material. The paper type is determined by utilizing that the surface roughness varies from recording material to recording material and each recording material has different glossiness. In other words, the type of the recording medium is identified by comparing glossiness data acquired by measuring the specularly reflected light with a pre-stored threshold value. In this case, a detection error occurs when there is a variance in light receiving sensitivity at which reflected light is received. Hence, light is irradiated from a light-emitting portion in several different light-emitting amounts, and the type of the recording medium is identified according to a light receiving amount received at the light receiving portion when light is irradiated in a specific light-emitting amount.
These inventions use a CMOS sensor or plural light receiving elements, which complicates the device configuration and increases the cost. In addition, each is based on the technique to determine the type of paper using reflected light from the surface of paper. However, because this method is affected by the surface condition of paper, none of these inventions is fully acceptable as paper type determination means.